@Edent there are a few instances that can talk to activitypub instances on tor(like mine). There are 13 known activitypub instances on tor and probably none on i2p. https://fedilist.com/instance?q=&ip=&software=&registrations=&onion=only
Considering that mastodon has a entire doc page for running mastodon on tor there are very few instances and most of them are mitra. Most instances apparently can be accessed from tor but requiring a email kinda defeats the anonymity. Personally I prefer to not have tor users register on my main instance since they are also less modarable.

Btw I'm the guy from gitlab who made the issue